In the treatment of motion sickness, traditional remedies have relied predominately upon drugs in the antihistaminic and anticholinergic drug classes. See e.g. Money, Psychological Reviews, 50(1):1-39(1970); Wood et al., Aerospace Med. 43(3):249-252(1972); and Wood et al., Aviation Environ Med. 58(9 Supp.): A262-5(1987). Examples of these drugs include promethazine, scopolamine, dimenhydrinate, and cyclazine, and sometimes these compounds are combined with a sympathomimetic agent such as ephedrine or amphetamine to enhance their action and to reduce the side effects such as lethargy or drowsiness that often accompany the use of these drugs. Other side effects that often accompany the drugs used in the prevention of motion sickness have been blurred vision, dizziness, dryness of mouth and sedation. Thus, therapies using the present day anti-motion sickness drugs, either alone or in combination with other drugs, have been less than optimal.
More recently, it has been discovered that certain anticonvulsant agents are useful in methods to prevent or treat motion sickness. For example, in U.S. Pat. No. 4,992,443 (Chelen), a method of treating motion sickness is disclosed wherein the patient is administered an effective amount of a particular anticonvulsant compound such as diphenylhydantoin (or phenytoin), ethotoin, or primidone. Although these compounds avoid many of the problems present in the prior traditional methods for treating motion sickness, it is still a highly desirable object to reduce the amount of anticonvulsant that can effectively be administered to a patient to control motion sickness to a bare minimum so as to minimize or eliminate entirely the likelihood of side effects from the anticonvulsant compound.
Recently, researchers have revealed a brain receptor interaction between certain anticonvulsant compounds such as phenytoin and antitussives or cough supressant agents such as dextromethorphan. See Tortella et al., Brain Research. 383:314-318(1986). In addition, several U.S. patents including U.S. Pat. Nos. 4,694,010 and 4,898,860 (Musacchio et al.) and U.S. Pat. No. 4,906,638 (Pontecorvo et al.), disclose the use of an antitussive compound such as dextromethorphan in combination with anticonvulsant compounds in order to achieve anti-epileptic effects and control seizure. However, these references do not disclose or suggest use of the antitussive agents in the treatment of motion sickness.
It is thus a highly desirable object to develop methods of treating motion sickness through the use of reduced amounts of anticonvulsant agents which can be administered safely, conveniently and effectively in treating and/or preventing motion sickness.
It is thus another object of the present invention to prevent or treat motion sickness using an anticonvulsant compound in combination with a potentiating agent which allows successful use of a reduced amount of the anticonvulsant compound in the treatment of motion sickness with a resulting reduced risk of side effects as well.